 The plates move at a relative rate of over 0.4 inches (10 mm) per year at a somewhat oblique angle to the subduction zone.Because of the very large fault area, the Cascadia subduction zone can produce very large earthquakes, magnitude 9.0 or greater, if rupture occurred over its whole area.When the "locked" zone stores up energy for an earthquake, the "transition" zone, although somewhat plastic, can rupture.